Summary:
PgaB is an outer membrane lipoprotein that is required for the partial de-N-acetylation and transport of poly-β-1,6-N-acetyl-D-glucosamine (known as PGA or PNAG) - an exopolysaccharide that is a key component of the biofilm matrix of several medically important bacteria [Wang04b, Itoh05, Itoh08].

PgaB consists of an N-terminal domain that forms a (β/α)7 barrel structure and belongs to the class 4 carbohydrate esterases and a C-terminal domain that forms a (β/α)8 barrel and contains a flexible β hairpin loop [Little12]. Both domains are necessary for de-N-acetylation of PNAG; PNAG binds to a cleft formed between the N and C-terminal domains in an extended conformation [Little14].

PgaB is a metal dependent de-N-acetylase with a preference for Co2+, Ni2+ and Fe2+; PgaB binds two metal ions per molecule; PgaB has specificity for PNAG oligomers [Little12]

Deletion of pgaB results in reduced biofilm formation and retention of acetylated polymer in the periplasm; deacetylation of PNAG by PgaB promotes its export [Wang04b, Itoh08].

pgaB is part of a 4 gene locus (pgaABCD) whose gene products are involved in the synthesis, modification and export of PNAG. Expression of pgaABCD is higher at 37°C than at 21°C and is highest during stationary phase [Cerca08]. Expression also increased in response to one-percent NaCl or ethanol [Cerca08]. Expression increased in response to glucose, ethanol, NaCl, and MnCl2 in a clinical isolate, and dramatically increased upon deletion or mutation of csrA in this strain [Cerca08, Mercante06]. CsrA inhibits translation of pgaABCD mRNA by binding to six sites within the pgaABCD leader [Wang05b, Mercante06]. NaCl and alkaline pH induction are dependent upon nhaR as deletion of this gene prevented induction [Goller06, Cerca08].

PgaB has similarity to the HmsF protein encoded by the Yersinia pestis hmsHFRST gene cluster, which is involved in plague transmission [Jones99].